1. Field of the Invention
The present invention relates to steering gear assemblies and, more particularly, to rack and pinion steering gear assemblies having at least one rack bushing.
2. Description of the Related Art
Conventional rack and pinion steering gear assemblies, whether manual or having an electric or hydraulic power assist, typically include a bushing that provides a low friction-sliding surface for rack translation along a Y-axis and rotation about its centerline while supporting the rack in the X and Z directions in a mutually perpendicular X-Y-Z coordinate system. Rack bushings are typically installed in the gear assembly housing bore opposite the pinion end and are often retained by a snap fit into a groove formed in the housing bore, by being press fitted into the bore, or, by the use of a separate snap ring retainer.
Many known rack bushing designs employ a generally cylindrical shape having a closed and continuous periphery. Oftentimes, such bushings are made of well-known self-lubricating materials, such as, for example, acetal. One example of such a known rack bushing is shown in FIGS. 1-6. The prior art steering gear assembly 10 of Figure includes a housing 12 in which a rack (not shown) is positioned. A rack bushing 14 is located within the internal bore of housing 12 and includes two sets of slots 16, 18 that extend longitudinally from opposite ends of bushing 14. The slots 16, 18 are provided to facilitate the radial expansion and contraction of bushing 14. A radially extending projection 15 is used to engage a recess located in the housing bore and secure bushing 14 within housing 12. Prior art bushing 14 is shown in several views in FIGS. 3-6. Such a bushing, however, does still tend to encounter hoop stresses which limit such radial expansions and contractions. Mena discloses another prior art rack bushing that has similar front and rear slots in U.S. Pat. No. 6,485,180 B2, the disclosure of which is expressly incorporated herein by reference.
In rack and pinion steering gears having a bushing with a closed periphery encircling the rack and located between the rack and the housing within the housing bore, clearances will generally be provided between the rack and the bushing and between the bushing and the housing to accommodate manufacturing tolerances and thermal expansion. Clearances between the bushing and rack or between the bushing and housing, however, can, in certain driving conditions, create objectionable rattle noise that can be heard by the driver and passengers. Such objectionable noise tends to grow louder as the bushing wears and the clearances increase and is the source of significant warranty issues. Those steering gears having a high inertia above the steering gear often suffer from such objectionable noises and non-assisted standard manual rack and pinion gears and column assist and single pinion assist electric power steering systems are particularly susceptible to such objectionable noises. Hydraulic gears are not as susceptible to such rattle noises as manual gears, but the concern with such objectionable noises may still be present in such applications.